In electrostatographic printing, commonly known as xerographic printing or copying, an important process step is known as “fusing”. In the fusing step of the xerographic process, dry marking making material, such as toner, which has been placed in imagewise fashion on an imaging substrate, such as a sheet of paper, is subjected to heat and/or pressure in order to melt and otherwise fuse the toner permanently on the substrate. In this way, durable, non-smudging images are rendered on the substrates.
The most common design of a fusing apparatus as used in commercial printers includes two rolls, typically called a fuser roll and a pressure roll, forming a nip therebetween for the passage of the substrate therethrough. Typically, the fuser roll further includes, disposed on the interior thereof, one or more heating elements, which radiate heat in response to a current being passed therethrough. The heat from the heating elements passes through the surface of the fuser roll, which in turn contacts the side of the substrate having the image to be fused, so that a combination of heat and pressure successfully fuses the image as shown, for example, in U.S. Pat. Nos. 5,452,065; 5,493,373; and 7,460,822 B2.
Belt fusers are a type of fuser apparatus in which an endless belt is looped around a belt guide. A pressure roller presses a sheet having a toner image onto the fuser roller with the endless belt intervening between the pressure roller and the fuser roller. The fixing temperature for the toner image is controlled on the basis of the temperature of the fuser roller which may be detected by a sensor, such as a sensor in the loop of the belt and in contact with the fuser roller. A nip region is formed on a pressing portion located between the fuser roller and the pressure roller. The belt on a belt fuser is typically short as the fuser assembly is often enclosed within a cassette, and it is desirable that such a fuser cassette is as small as possible. Examples of belt fusers are shown, for example, in U.S. Pat. Nos. 7,228,082 B1, 7,986,893 B2 and 8,121,528 B2.
One configuration for radiating heat is a resistive heater that is adapted for heating a fuser belt with the heater comprising a heating board made of a ceramic, such as aluminum nitride, and a resistive trace formed over the heating board, with the heating board transferring heat from the resistive trace to the fuser belt. For example, resistive traces were provided on aluminum nitride surface, and heat was generated in the traces (the resistive layer) that had to then migrate from the resistive layer to the aluminum nitride surface and then from the aluminum nitride surface to heat the belt. It was this complex heat transfer that provided the heat to the fuser belt to facilitate the fusing function undertaken by the fuser belt. As shown in U.S. Pat. No. 7,193,180 B2, for example, a resistive heater is disclosed that is adapted for heating a fuser belt with the heater comprising a substrate, a first resistive trace formed over the substrate, and a second resistive trace formed so as to at least partially overlap the first trace. Another configuration for radiating heat inside the fuser roll or belt is to use a lamp configured to heat the heating board. These fuser solid heater elements are comprised of high cost base materials and inks manufactured in a time consuming process and require complex control strategies for axial temperature control and pre-warming to prevent belt stalling.
Metallic and ceramic materials are known to have excellent heat conduction properties and increased ability to withstand thermal breakdown when continuously exposed to elevated temperatures, it is these materials that are known to best suit themselves to use in high temperature heat generation elements such as those used in fuser units. In particular designs, heat rolls are added to adequately dissipate excess heat generated according to the heating process. However, for the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for new heating element design in electrostatographic printing. It would be a benefit if such designs effectively mediate any need for heat rolls and other additional structures. There is also a need for improved independent control of a heating element.